Light emitting diode (LED) lamps have been developed to replace conventional incandescent or fluorescent lamps for reducing electrical and maintenance costs, and for increasing reliability. LED lamps consume less electrical energy than conventional lamps while exhibiting much longer lifetimes. Such LED lamps typically include a power supply and a plurality of LEDs mounted on a flat or curved surface.
One growing use of LED lamps is the replacement of incandescent light bulbs in traffic signal lamps. A common conventional traffic signal lamp is illustrated in FIGS. 1A and 1B, and includes a housing 1, a front door plate 2, a lens 3, a reflector 4 and an incandescent light bulb 5. Retainers 6 affix the lens 3 to the front door plate 2, which opens via hinges 7 to allow access to the interior of the housing 1. Light bulb 5 screws into electrical socket 8, which is electrically attached to a terminal strip 9, which in turn receives its power from the traffic signal controller.
It is known to replace the incandescent light bulb 5 with an LED lamp, along with the lens 3 since it is designed for the output of an incandescent light bulb. In a conventional traffic signal lamp retrofit procedure, the lens 3, light bulb 5, reflector 4 and socket 8 are all removed, and an LED lamp module 10 is installed to the front door plate 2 to replace lens 3, as illustrated in FIG. 2. Wires 11 from the LED lamp module are connected to the terminal strip 9.
The above mentioned retrofit method has several drawbacks. First, it is time consuming and labor intensive to remove the reflector 4 and socket 8, and access the terminal strip 9 with new wiring. Because traffic is usually blocked in order to access traffic lights, time is of the essence. Second, in order to safely disconnect the socket connector wires from the terminal strip, and connect new wires from the LED lamp module 10 to the terminal strip, the power to the traffic signal must be temporarily turned off, which disrupts traffic flow through the intersection. Finally, once the retrofit is complete, it is not possible to put the original incandescent lamp back in the traffic signal lamp, for example in case a spare LED lamp is not available.
One solution is to insert an LED lamp that utilizes the reflector 4 and socket 8, thus negating the need for their removal, as taught by U.S. Pat. No. 6,796,698. Here, a specially designed LED light source screws directly into the socket connector. The drawbacks to this solution are that the reflector can introduce light loss (especially when contaminated by dirt or deteriorated with age), reflectors can vary among manufacturers necessitating varying LED light source designs, and the LED light source design is complicated and expensive.
Another solution is to utilize a lamp module that mounts to the front door plate of the signal light housing, with a threaded electrical connector compatible with the socket connector, as taught in U.S. Pat. Nos. 6,268,801 and 6,905,227. This solution involves removing the conventional lens and light bulb source, mounting the lamp module to the front door plate, and connecting the threaded electrical connector to the socket connector, which avoids the use of the reflector (and any associated light loss therefrom) while also avoiding the removal of the reflector and socket electrical connector. However, it still requires lens removal and module mounting to the door.
An even simpler solution is the use of an LED lamp with a threaded electrical connector compatible with the socket connector, where the socket connector not only supplies the electrical power, but also provides the sole mechanical support for the LED lamp in the traffic signal housing, as taught in U.S. Pat. No. 6,911,915. Here, the conventional lamp is simply replaced with the LED lamp having the same electrical connection, and a Fresnel lens is mounted to the door that collimates the light so that it just fills and illuminates the outer lens of the traffic signal lamp. The use of the reflector (and any associated light loss) is avoided. Subsequent lamp changes simply involve swapping one LED lamp with another. However, even here there are possible complications. Alignment between the LED lamp and Fresnel lens is important because of the directionality of the light output of the LED lamp (and the avoidance of using the reflector). For traffic signal lamps where the socket connector does not adequately align the LED lamp with the Fresnel lens, light can be wasted (by missing the Fresnel lens), and even illumination of the outer lens may not achieved. Improper socket connector alignment can be a function of inadequate initial alignment or quality control, fatigue with age, extreme shaking (e.g. from wind), or even inadequate mechanical support of the socket connector for supporting the weight of the LED lamp (e.g. the LED lamp sags downwardly after installation and/or with time).
There is a need for a lamp design that reliably aligns and secures an LED lamp to the associated lens(es) while still providing easy removal and installation of the LED lamp.